docs: def load_sst(path=None,
               url='http://nlp.stanford.edu/sentiment/trainDevTestTrees_PTB.zip'):
      """
      Download and read in the Stanford Sentiment Treebank dataset
      into a dictionary with a 'train', 'dev', and 'test' keys. The
      dictionary keys point to lists of LabeledTrees.
  
      Arguments:
      ----------
          path : str, (optional defaults to ~/stanford_sentiment_treebank),
              directory where the corpus should be downloaded (and
              imported from).
          url : str, where the corpus should be downloaded from (defaults
              to nlp.stanford.edu address).
  
      Returns:
      --------
          dict : loaded dataset
      """
      if path is None:
          # find a good temporary path
          path = os.path.expanduser("~/stanford_sentiment_treebank/")
          makedirs(path, exist_ok=True)
      fnames = download_sst(path, url)
      return {key: import_tree_corpus(value) for key, value in fnames.items()}